The vomeronasal system is one of several nasal chemoreceptive systems present in terrestrial vertebrates. It is a major source of direct exteroceptive information to the limbic system and has been implicated, over the past 10 to 15 years in several species-typical behaviors. Over the past 12 years our laboratory has gathered evidence for the importance of the garter snake vomeronasal system in a variety of behaviors including prey extract trailing, prey extract attack, aggregation, shelter selection and male response to female sex pheromones. Most recently we have established that a vomeronasally mediated stimulus can be intrinsically reinforcing and have identified a substance in earthworm wash, earthworm cuticle collagen, which is a snake chemoattractant whose detection is mediated via the vomeronasal system. The current proposal extends these studies and expands the domain of interest to a marsupial, Monodelphis domestica, the grey short tailed opossum. The new studies will include further purification of the chemoattractant in earthworm wash, and identification of that portion recognized by the vomeronasal system of the garter snakes; characterization of a second garter snake chemoattractant, earthworm alarm pheromone; continued behavioral and electrophysiological analysis of olfactory vs. vomeronasally mediated chemosignals in snakes and development of behavioral tasks for electrophysiological analysis of opossum response to marking pheromones.